1. Field of the Invention
This invention relates to the field of heating systems for dwellings and the like, and in particular to hot water heating systems employing solid fuel and having a reservoir to store generated heat.
2. Description of the Prior Art
A wide variety of systems useful as wood burning heaters and hot-water-based heaters are available on the market. All such systems require some form of combustion area or heat generating area and some form of heat exchanger to transfer the generated heat to the heat transfer fluid which is then circulated to remotely located radiator units. Beyond these matters in common, there are a number of variations, each of which will affect utility in different environments.
Prior art systems have been based upon both steam and hot water. In steam systems, boiler tubing was often employed in order to produce steam without the necessity of heating the entire reservoir to the point of boiling. Accordingly, in steam systems, relatively small reservoirs generally sufficed, and usually were not used to store heat. More recent systems, however, employ hot water as a heat transfer medium. Such systems also have boilers, and usually have a reservoir, the boiler contents often constituting the reservoir. Although hot water systems may be run at substantially lower temperatures than steam systems, there are certain problems with incidental generation of steam and also with the variation in the volume of gas (i.e., air) dissolved in the water at different temperatures. Additionally, heat transfer fluid will expand somewhat when heated. These matters each cause variations in the total volume of heat transfer fluid which must be accomodated. The variation in volume due to temperature variation is proportional to reservoir volume, and stresses due to excessive pressure may cause a sealed system to fail. Although resilient expansion means and overflow storage tanks form a part of the art, very large reservoirs have not been employed due to such expansion problems.
With regard to the fuels used in prior art systems, it has recently become popular to employ solid fuel systems based for example on wood or coal. Wood and coal were, of course, the most common of fuels in former years. Nevertheless, the relatively inefficient designs of fireplaces and coal burning stoves from such former years have been largely abandoned. Current solid fuel burning apparatus tend to be highly sealed, and an effort is made to extract heat from the fuel slowly by limiting the flow of combustion air. Efficiency is not sought merely in order to conserve solid fuel resources. It should also be kept in mind that a more efficient system will require the user to store less fuel to heat a given space for a given time. Accordingly, savings in storage space and in user effort may be expected as well.
Attempts to increase the efficiency of solid fuel heating apparatus have not been entirely successful for reasons not directly related to efficiency of combustion. Many designers have opted for maximum efficiency at the expense of convenience and durability. The prior art teaches that efficiency may be expected to increase where a large number of heat exchangers having relatively large surface area are disposed very close to the hottest part of the combustion area. Similarly, the art teaches that increased efficiency may be expected where the combustion area is sealed and insulated to the maximum extent possible. Accordingly, designers are tempted to seal numerous heat exchangers of high thermal conductivity (e.g., copper) inside air-tight combustion areas swathed in a great deal of insulation. Prior art systems then route heat transfer fluid from the maze of heat exchangers either to and from the radiators or a relatively small but well insulated reservoir.
Of course, such tightly sealed and blanketed heat generation, storage and transfer apparatus are difficult to maintain. Creosote develops on the cooler surfaces of heat exchangers, metals of high thermal conductivity tend to corrode rapidly; varying rates of thermal expansion gradually force open joints; and, any maintanance is virtually impossible due to the complication of piping and insulation layering employed.
Accordingly, there has been a need for a very simple construction of very durable material that nevertheless exhibits a high efficiency. A system has been needed that is easily maintained and serviced in all aspects of operation. The desired system should be easy to load and empty, easy to clean, and easy and inexpensive to construct. The system should be highly efficient, and should capture and store virtually all the heat available, but the user should not be burdened with multiple heat exchangers and extensive insulation which interfere with access to system parts.
Another consideration concerns the amount of heat which may be stored in systems of various design. Large heat storage capacity would seem to imply a large reservoir. But fireplaces themselves are relatively large constructions, and if the user of a fireplace-type heat generation system is expected to devote a large volume in addition to the fireplace to the heating system, such a system would never become popular. Accordingly, there has been a need to make a very efficient use of the space allotted to a heating system. The combustion area and the reservoir of heat transfer fluid should be large enough to generate and store all the heat necessary for at least a full day, and the fireplace should be large enough to be conveniently loaded with pieces of fuel of a conveniently large size. According to prior art teachings, such requirements would necessitate devoting half the space of a standard basement to a reservoir and fire area. The present invention provides the necessary large dimensions, but does so in an efficient manner.
The present invention both conserves space and increases efficiency by immersing the entire combustion chamber in a huge reservoir of heat transfer fluid. Only such openings as are required for convenient servicing of the combustion area, e.g., loading fuel, removing ashes, supplying air and removing exhaust are provided. The system is extremely durable and is constructed entirely of heavy boiler plate materials. Like some prior art systems, boiler tubes communicating with the fluid reservoir are provided, in an upper portion of the combustion area, and in a more intimate relation to the burning fuel, doubling as fuel supports. Shaker grids interleaved with the lower boiler tubes permit the user to agitate the burning fuel, and ashes which drop therefrom are easily removed from a portal provided for that function. A heat exchanger integral with the flue extracts the last bit of heat from the escaping gases, using an arrangement having unconventional fins located on the fluid side of a gas/fluid heat exchanger. The flue is easily cleaned since the inner surface of the flue pipe is smooth and easily brushed or scraped clean.